In research into chemical reactions, high throughput experimentation is widely used. In high throughput experimentation, a plurality of relatively small scale reactors is placed in parallel. In each reactor, a different experiment takes place. Usually, conditions and/or reactants are varied slightly over the different reactors. For example all reactors are operated at the same pressure and temperature, but all contain a different reactant, or the reactants are all the same, but pressure and temperature are varied. After the experiments are carried out, the results of the experiments are compared with each other, and for example interesting reactants (e.g. catalysts) or promising reaction conditions are identified. Carrying the experiments out in parallel leads to a significant reduction in the time it takes to come up with experimentation results.
Usually, in high throughput experimentation, the reactors are small, as are the amounts of reactants that are used. If flow through reactors are used, the flow rates of the fluid flows are also low. Typical reactor sizes do not exceed 1 cm in diameter, and when for example catalytic activity is tested, typically a few grams of a potential catalyst are present in each reactor. Sometimes even less potential catalyst is used, e.g between 0.005 and 1 gram. Flow rates are usually less then 10 ml/hour for liquids and/or less than 150 Nml/minute for gas. The typical low flow rate used in high throughput reactions makes controlling the fluid flow through the individual reactors hard.
In order to be able to compare the results of the experiments that are carried out in the different reactors with each other, it is important to know the process conditions under which each experiment took place. Such process conditions include e.g. temperature, pressure and flow rate.
WO99/64160 aims at keeping the flow rate the same through all reactors by providing a passive flow restrictor upstream or downstream of each reactor. The resistance to fluid flow in each restrictor is so high that it is the restrictor that determines the flow rate through each reactor. Passive flow controllers usually are cheaper and compacter than active flow controllers. On the other hand, active flow controllers allow for adjustment of the flow during the experiment, without having to interrupt the experiment.
A disadvantage of using flow restrictors as passive flow controllers to control flow rate through the reactors is that all flow restrictors have to be calibrated individually in order to obtain the desired flow distribution over the reactors. When for example capillaries are used as flow restrictors, the length of the capillaries has to be changed in order to get the right resistance to fluid flow. This is labour intensive.
U.S.2004/0121470 describes a method and apparatus for high throughput catalysts screening and optimization. In this method and device, multiple parallel reactors are provided, but the experiments take place sequentially. While one reactor is fed with a reactant gas and/or liquid, the other reactors are fed with an inert fluid, and/or a fluid for pre-treatment, regeneration or the like. The effluent coming from the reactor in which the experiment takes place is supplied to an analyzer. When the experiment is done, a different reactor is fed with the reactant fluid and the previously active reactor receives the other fluid (inert, pre-treatment, regeneration, etc.).
The known apparatus comprises a rotary valve upstream of the reactors, which valve ensures that the reactant fluid is directed to one reactor and the other fluid (inert, pre-treatment, regeneration, etc.) is directed to the other reactors. So, in the known apparatus, the valve upstream of the reactors is used to determine which reactor receives which fluid.
The object of the invention is to provide an improved system and method measuring flow rates of parallel fluid flows.
This object is achieved with the systems and the methods of the present invention.
In accordance with the invention, a fluid flow is distributed over a plurality of reactors. These reactors are preferably flow through reactors, but it is also possible to use the invention during the filling of a plurality of batch reactors.
The flow can be distributed equally over the reactors, but it is also possible that a different flow distribution is desired, e.g. the first reactor receiving x ml/min, the second reactor receiving 2x ml/min, the third reactor receiving 3x ml/min etc. The skilled person will understand that any predetermined flow distribution can be used in the invention.
In accordance with the invention, a common feed line branches out into a plurality of reactor feed lines. The reactor feed lines receive fluid from the common feed line. Through the common feed line flows a combined fluid flow, which is split into reactor feed flows, each of which reactor feed flows flowing to a reactor. The fluid of the combined feed flow and the reactor feed flows can be gas, liquid or a combination thereof. Each reactor feed line leads the received fluid to the reactor that is connected said reactor feed line. It is possible that multiple reactor feed lines are connected to each reactor. This makes it for example possible to supply both a liquid and a gas to the reactors.
In addition to the reactor feed lines, the system also comprises a measurement line. The measurement line branches out, such that it has multiple outlets. Each outlet is connected to an associated reactor feed line.
In a first embodiment, the measurement line has a single inlet. In this embodiment, the measurement line inlet is connected to the common feed line.
In a second embodiment, the measurement line has multiple inlets. In this embodiment, each of the measurement line inlets is connected to an associated reactor feed line. In each reactor feed line, the connection with the measurement line inlet is arranged upstream of the connection with the measurement line outlet.
In the measurement line, a first flow sensor is arranged. This flow sensor is adapted to measure the flow rate of the fluid flowing through the measurement line. The flow sensor can be any suitable kind of flow sensor. It is however preferred that a flow sensor is used that has a low resistance to fluid flow, such as a flow sensor that is based on the time of flight principle. It is also possible to use other suitable types of flow sensors.
Further, the system according to the invention comprises a valve system. The valve system comprises one or more valves and a valve control unit for controlling the one or more valves, in particular controlling the setting of the one or more valves. The valve system is arranged and/or adapted such that it can assume a non-measurement setting which allows the fluid coming from the common feed line to flow into the reactor feed lines that are connected to the common feed line and via the reactor feed lines into the reactors. In this non-measurement setting, the fluid flows flow through the entire reactor feed lines. When the valve system is in its non-measurement setting, the flow rate is not measured by the flow sensor in the measurement line.
The valve system can also assume a measurement setting, in which the valves redirect one of the reactor feed flows such that it flows through the measurement line. While this redirected reactor feed flow flows through the measurement line, the reactor feed line it would flow through when the valves were in their non-measurement setting, is blocked. This (temporarily) blocked reactor feed line is bypassed completely or partly by the measurement line.
When the valve system is in its measurement setting, the valve control unit preferably changes the settings of the valve or valves such that sequentially, one after the other, fluid flowing to or into each reactor feed line is redirected to flow through the measurement line and that the redirected flow flows through the measurement line. So, one after the other, the flow rate of the fluid flow of one reactor feed line is measured by the first flow sensor.
During a measurement cycle, each reactor feed flow is redirected through the measurement line once. So, one after the other, the flow rate of each reactor feed flow is measured by the flow sensor in the measurement line.
Preferably, a plurality of measurement cycles is carried out during the course of the experiments. There can be a time interval between successive measurement cycles, or the measurement cycles can be performed right after each other. Also, there can be a time interval between the measurements in a measurement cycle, or the measurements in a measurement cycle can be performed one right after the other.
The valve system can comprise any suitable kind of valve. It is possible to use individual valves for each individual line (each valve having a single inlet and a single outlet), but it is also possible that rotary valves are used which act on the fluid flows in or to a plurality of lines at the same time. Such a rotary have has therefore multiple inlets and multiple outlets.
An advantage of the system and method according to the invention is that only the measurement line needs to be provided with a flow sensor but still the flow rates in all individual reactor feed lines can be measured. This of course reduces the costs as less flow sensors have to be present. An other important advantage in using a flow sensor only in the measurement line is that all measurement are carried out by the same flow sensor. Therewith, extensive calibration is no longer necessary. If multiple flow sensors are used, one in each reactor feed line, and you would want to compare the flow rates of the different reactor feed lines, you must make sure that the readings of all flow sensors are accurate enough for a reliable comparison. In practice, this boils down to that all flow sensors have to be individually calibrated against the same standard. In the system and method according to the invention this is no longer necessary, as for all measurements the same flow sensor is used.
In a possible embodiment, the flow rate is not just measured in the measurement line, but also the flow rate through the common feed line is determined. This flow rate can be measured by a flow sensor of any suitable type that is arranged in the common feed line. In practice it has been found that a coriolis flow sensor works well. Alternatively (or even in addition) a simple mass gauge can be used that measures the reduction of the mass of the fluid source that is caused by the fluid flowing out of the fluid source. The mass reduction over time can be correlated to the flow rate of the fluid out of the fluid source and into the common feed line.
In a further possible embodiment, in addition to the measurement line upstream of the reactors, a second measurement line is present downstream of the reactors. This second measurement line has multiple inlets. Each inlet of the measurement line is connected to one of the effluent lines coming out of a reactor.
In such an embodiment, second valves and a second valve controller are present to make sure that flow is redirected from a first effluent line through the second measurement line so that its flow rate can be measured. Successively, the flow of each effluent line is directed through the second measurement line such that all flow rates can be determined. This information can for example be used to determine catalyst activity or reaction efficiency.
In an advantageous embodiment, the measurement system according to the invention is used in the control of the flow rates of the fluid flows to the reactors.
In such an embodiment, each reactor feed line comprises a flow controller. This flow controller is an active flow controller, which means that the flow rate of the fluid flow passing through it can be adjusted without having to interrupt the experiment. Examples of suitable active flow controllers are heat controlled flow restrictors (e.g. heat controlled capillaries or heat controlled pinholes), needle valves or mass flow controllers.
Such an embodiment further comprises a flow control unit for controlling the flow rate of the fluid flow through the reactor feed lines. The setting of the flow controllers in the reactor feed lines is determined on the basis of the measurement results of the first flow sensor that is arranged in the measurement line.
In a further embodiment it is possible that two or more flow sensors are arranged in the measurement line. These two flow sensors can be arranged in series or in parallel.
For example, one flow sensor can serve as a redundant flow sensor, a back up in case the other one fails. In such a system, it is advantageous to arrange the flow sensors in parallel, and have a valve system that directs the full flow through the measurement line through one of the flow sensors. Should this flow sensor fail, the valve system changes the setting of the valves such that the flow is directed through the other sensor. The failed sensor can then be replaced without shutting down the system, and therewith without having to interrupt the experiments.
As an alternative or in additional, two or more flow sensors can be arranged in parallel in the measurement line. The flow sensors can be used as a double check, or they can have a different measurement range.